What is Cap Drag?
Cap drag is an issue that arises when either the closure thread dimensions (T and E) are too small or the bottle thread dimensions (T and E) are too large. For many years, the thread dimensions of different neck finishes used in the industry have been published by the Plastics Industry Association (formerly known as Society of the Plastics Industry). The threads published are standard and are designed to work with the closure thread dimensional sizes that the Closure & Container Manufacturers Association (now part of the International Society of Beverage Technologists) published.
If a bottle or closure has a 24mm finish, it can be assumed that it will be identical to all 24mm finishes, making such finishes universally compatible. However, this is not the case. If the details of a bottle and closure finish are not complying with the standards, there’s a chance that cap drag might occur. This is why all drawings should be reviewed and all components tested together to be sure compatibility before you end up with a warehouse full of unusable stock.
How does Cap Drag happen?
When a closure is too small, the T and E dimensions of the bottle will rub against the T and E dimensions of the closure, creating the friction called cap drag. If this happens on a fill line, it will potentially create false application torque. This can result in leaky packaging, since there’s a high chance that the closure may not have been applied all the way, meaning there’s not a seal.
How can I avoid Cap Drag?
It is a good idea to have your drawings reviewed before project commencement, to avoid any cap drag issues. Test all component samples together (with product) prior to ordering. Make sure that your component suppliers are also conducting regular quality control checks during production run, to ensure these parts adhere to the drawing specs.